1. Field of the Invention
The present invention relates to an inner shaft supporting apparatus of a vehicle power train. More particularly, the present invention relates to an inner shaft supporting apparatus of a vehicle power train, which can improve noise and vibration limitations by improving the natural frequency and the dynamic stiffness of a bracket assembled to support a bearing of the inner shaft.
2. Description of Related Art
A power train of a vehicle denotes all apparatuses that are connected in a process of delivering power generated in a power unit to a drive wheel, and includes a clutch and a transmission, a shaft (output axis), a final reduction gear, and differential gears.
The term ‘power train’ refers to apparatuses that generate power and deliver it, and is being used as a meaning including an engine or a drive motor that actually generates power.
FIG. 1 is a perspective view illustrating important components among a power train of a vehicle, which include an engine 1, a transmission 2, an inner shaft 3, and a drive shaft 4. In the case of an electric vehicle, the engine and the transmission are replaced with a drive motor and a decelerator.
In the above configuration, the inner shaft 3 has an end portion coupled to a side gear of the transmission 2 or the decelerator by a spline coupling method so as to receive power, and another end portion coupled to the drive shaft 4 via a constant velocity joint so as to deliver power.
In the power train of a vehicle, the inner shaft 3 is mounted in the engine 1 using bearings and brackets. Hereinafter, a supporting apparatus of the inner shaft 3 will be described as follows.
FIG. 2A and FIG. 2B are perspective views illustrating an inner shaft and a supporting apparatus thereof. The supporting apparatus 10 is a structure for rotatably supporting and coupling the inner shaft 3 to the engine 1, and includes a bracket 11 and a bearing 15.
Referring to FIG. 2A and FIG. 2B, the supporting apparatus 10 including the bracket 11 and the bearing 15 is mounted at the end portion of the inner shaft 3 connected to the drive shaft 4 through the constant velocity joint. In this case, the inner shaft 3 is press-fitted into the inner ring 16 of the bearing 15, and the outer ring 17 of the bearing 15 is press-fitted into a bearing coupling part of the bracket 11.
Also, the end portion of the bracket 11 is fixedly coupled to the coupling part 1a of the engine using bolts. Finally, the one end portion of the inner shaft 3 is coupled to the transmission 2 or the deceleration to be supported, and another end portion of the inner shaft 3 to which the constant velocity joint is coupled to the engine 1 to be supported by the supporting apparatus 10, i.e., the bracket 11 and the bearing 15.
FIG. 3A and FIG. 3B are views illustrating a bracket of a typical inner shaft supporting apparatus, and FIG. 4A, FIG. 4B, FIG. 4C and FIG. 4D are views illustrating various examples of a bracket of a typical inner shaft supporting apparatus.
FIG. 3A and FIG. 3B and FIG. 4A, FIG. 4B, FIG. 4C and FIG. 4D illustrate examples of typical brackets 11. As shown in FIG. 4A, FIG. 4B, FIG. 4C and FIG. 4D, the brackets 11 somewhat differ from each other in detailed shape, but are configured to have a structure in which the upper part or the lower part of the bracket 11 can be coupled to the engine 1 by bolts.
Referring to FIG. 3A and FIG. 3B, an upper three-piece coupling structure (a and c) and an upper two-piece coupling method (d) in which bolts are coupled to the upper part of the bracket 11, and a lower three-piece coupling structure (b) in which bolts are coupled to the lower part of the bracket 11 are shown.
The bracket 11 shown in FIG. 3A and FIG. 3B has an upper three-piece coupling structure, where bolts are coupled to upper three apertures 11a for fixation with the engine coupling part and dowel pins are coupled to another two apertures.
The bracket 11 includes a coupling part 12 disposed at one side thereof to be coupled to the engine 1 that is a fixed structure and a bearing coupling part 13 disposed at another side thereof to be coupled to the bearing.
Accordingly, the bracket 11 supports the inner shaft 3 by a cantilever supporting method in which only an upper or lower part is coupled to the fixed structure (engine) based on the bearing center.
In this case, the bearing coupling part 13 of the bracket 11 is coupled to the outer ring 17 of the bearing 15 by the press-fit method, and the inner shaft 3 is coupled to the inner ring 16 by the press-fit method. The bracket 11 and the bearing 15 assembled by the foregoing method rotatably support the inner shaft 3 with respect to the fixed structure (engine).
Also, in the assembling of the inner shaft 3, the bracket 11 and the bearing 15 are first assembled into the inner shaft by the press-fit method, and then the integrated inner shaft 3, bracket 11, and bearing 15 is coupled to the transmission (or decelerator) 2 and the engine 1, respectively.
Meanwhile, although the rib shape of the bracket is optimally reinforced, a supporting apparatus according to a related art has a limitation in that the natural frequency of the bracket cannot increase due to the structural limitation of the cantilever supporting method. Accordingly, a separation from the excitation frequency of engine explosion is impossible, and thus a resonance of the bracket occurs due to the excitation of the engine explosion, causing noise and vibration.
As shown in FIG. 3A and FIG. 3B, the resonance allows the bracket 11 to vibrate in upward and downward directions, left and right directions, and forward and backward directions shown as arrows in FIG. 3A and FIG. 3B, delivering amplified (resonant) vibration to the vehicle body and thus generating noise.
Although the rib is reinforced in the cantilever-typed bracket, the target of the natural frequency is difficult to satisfy. Accordingly, noise and vibration limitations occur. Even though the target of the natural frequency is satisfied, the vibration is amplified when the natural frequency is close to the excitation frequency of the engine.
In order to overcome the foregoing limitation, the dynamic stiffness of the bracket needs to be increased, but there is a limitation on the cantilever structure in which only an upper or lower part of the bracket is coupled to the engine that is a fixed structure, and particularly, if implemented, the weight significantly increases.
Also, in order to overcome the limitation on the cantilever structure, a both-end supporting structure in which both upper and lower parts of the bracket are coupled needs to be applied. However, in the method in which the inner shaft 3, the bracket 11, and the bearing 15 are first assembled into one body and then finally assembled with the power train, the application of the cantilever structure is inevitable, and the application of both upper and lower parts coupling structure is difficult.
Under the operational conditions of the drive shaft 4, since the lifespan of the bearing is long when both of the inner ring 16 (inner shaft is press-fitted into) and the outer ring 17 (press-fitted into the bearing coupling part of the bracket) of the bearing 15 are assembled by the press-fit method, the inner shaft 3, the bracket 11, and the bearing 15 are coupled into one body, and then finally coupled to the power train.
The structure design and assembly are performed in consideration of the engine auxiliary machinery and accessories, and the exhaust system. In the assembly method, one end portion of the inner shaft 3 is coupled to the transmission 2, and then the bracket is rotated to be seated in an engine coupling part 1a. Thereafter, the bracket is fixedly coupled to the engine coupling part 1a by bolts, and then the drive shaft 4 and the inner shaft 3 are assembled.
FIG. 5 illustrates limitations according to a related art. FIG. 5A illustrates a bracket 11 having a both upper and lower parts coupling structure. FIGS. 5B and 5C show that an interference with an engine coupling part (boss at the side of power train) la that is a fixed structure occurs when the bracket with a both-end coupling structure rotates.
As shown in the drawings, the inner shaft 3, the bracket 11, and the bearing 15 are first assembled into one body, and then the bracket 11 is coupled to the power train (engine). In the both-end coupling structure, when the coupling part 12 of the bracket 11 is seated in the engine coupling part 1a, an interference between the coupling part 12 of the bracket 11 and the engine coupling part 1a occurs, making it impossible for the bracket 11 to rotate.
Accordingly, there is a difficulty in installing of the inner shaft first coupled with the bracket and the bearing. In order to overcome this assembly limitation, a bracket with a cantilever structure is being applied in a typical inner shaft supporting apparatus in spite of the disadvantages in terms of the natural frequency and the dynamic stiffness because the bracket with the cantilever structure can be rotated and seated without an interference with the engine coupling part.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.